CVS 4 - The Heart as a Pump

Question 1

What are the 4 valves of the heart + where are they located?
When do these valves open?
What is the typical pressure in the 4 chambers of the heart during diastole and systole?

Answer 1

1) Bicuspid (mitral) valve - between LV + LA
2) Tricuspid valve - between RV + RA
3) Aortic valve - between LV + aorta
4) Pulmonary valve - between RV + pulmonary artery

• AV valves open when pressure in atria exceeds ventricles
• Outflow valves open when pressure in ventricles exceeds atria
• LA = 8-10mmHg, RA = 0-4mmHg, LV = 120/10mmHg, RV = 25/4mmHg

Question 2

What are the typical values for HR + SV (and therefore CO) in a standard 70kg male?

Answer 2

HR = 70bpm
SV = 70ml/min 
CO = 4.9L/min

Question 3

How are cardiac myocytes interconnected electrically?
How do they contract in response to an AP?
How long is a cardiac AP?

Answer 3

• Via gap junctions between cells (acting as a functional syncytium)
• An AP causes a rise in intracellular Ca2+
• 280ms (relatively long due to plateau phase)

Question 4

What do the cusps of the AV valve attach to?

What is the role of these attachments?

Answer 4

• Papillary muscles via chrodae tendinae

- Prevents inversion of valves during systole

Question 5

Describe the spread of electrical activity through the heart during 1 cardiac cycle.

Answer 5

1) Pacemaker cells in SAN generate AP
2) Spreads over atria (atrial systole)
3) Reaches AV node is and delayed for 120ms
4) Spreads down the septum between ventricles
5) From ventricular myocardium inner surface (endocardial) to outer surface (epicardial)
6) Ventricles contract from apex up forcing blood out of outflow valves.

Question 6

What are the 7 phases of the cardiac cycle?

What is the total duration of 1 cardiac cycle?

Answer 6

1) Atrial contraction 2) Isovolumetric contraction 3) Rapid ejection 4) Reduced ejection 5) Isovolumetric relaxation 6) Rapid filling 7) Reduced filling
- At 67bpm - 0.9s

NB: - make sure you are able to interpret Wigger’s diagram (slide 11)

Question 7

Describe the events of phase 1 (atrial contraction) in relation to the Wigger’s diagram. Include whether the valves are open or closed.

Answer 7

• Relates to P-wave on ECG, relates to A-wave on LA pressure.
• This “atrial kick” accounts for final 10% of ventricle filling, other 90% occurs passively.
• At the end of this phase, ventricular volumes are maximal (EDV) - typically 120mL.
• AV valves are open, outflow valves are closed.

Question 8

Describe the events of phase 2 (isovolumetric contraction) in relation to the Wigger’s diagram. Include whether the valves are open or closed.

Answer 8

• Relates to QRS complex on ECG (ventricular contraction), rise in ventricular pressure causes AV valves to close (causing S1 heart sound/”lub”)
• Causes C-wave in LA pressure line.
• No change in ventricular volume as all valves are closed.
• All valves CLOSED.

Question 9

Describe the events of phase 3 (rapid ejection) in relation to the Wigger’s diagram. Include whether the valves are open or closed.

Answer 9

• Ejection from LV occurs when intraventricular pressure exceeds aortic pressure - causing aortic valve to open.
• Causes “X descent” dip after C-wave on LA pressure line + rapid decrease in ventricular pressure line.
• AV valves closed, outflow valves open.

Question 10

Describe the events of phase 4 (reduced ejection) in relation to the Wigger’s diagram. Include whether the valves are open or closed.

Answer 10

• Relates to “T-wave” on ECG (ventricular repolarisation)
• Relates to “V-wave” on atrial pressure line as pressure rises from continued venous return.
• AV valves closed, outflow valves still open

Question 11

Describe the events of phase 5 (isovolumetric relaxation) in relation to the Wigger’s diagram. Include whether the valves are open or closed.

Answer 11

• Intraventricular pressure falls below aortic, causing brief backflow of blood and closing of the aortic valve - causing S2 heart sound/”dub”.
• Relates to dicrotic notch in aortic pressure line
• Ventricular volumes remain the same as all valves are closed - this is ESV - typically 70-80mL
• all valves CLOSED

Question 12

Describe the events of phase 6 (rapid filling) in relation to the Wigger’s diagram. Include whether the valves are open or closed.

Answer 12

• Falling atrial pressure as ventricle fill - causes “Y-descent” on atrial pressure line.
• When atrial pressure exceeds intraventricular, AV valves open
• Ventricular filling usually silent, but sometimes can cause S3 heart sound (normal in children, sign of pathology in adults)
• AV valves open, outflow valves closed.

Question 13

Describe the events of phase 7 (reduced filling) in relation to the Wigger’s diagram. Include whether the valves are open or closed.

Answer 13

• Rate of filling slows (diastasis) as ventricles reach EDV
• 90% full by end of phase 7
• AV valves still open, outflow valves still shut

Question 14

What are the 2 ways in which valves can be abnormal?

Answer 14

1) Stenosis - valve doesn’t open enough, leading to obstruction to blood flow when valve is normally open.
2) Regurgitation - valve doesn’t close all the way, leading to leakage when valve should be shut.

Question 15

What are the causes of aortic valve stenosis and what are the 3 possible consequences?

Answer 15

Causes = degenerative (calcification/fibrosis), congenital or chronic rheumatoid fever.

1) LV hypertrophy due to increased LV pressure as blood can’t exit valve
2) Syncope - due to left sided HF
3) Angina - due to left sided HF

Question 16

What are the causes and consequences of aortic valve regurgitation?

Answer 16

Causes = aortic root dilation, or valvular damage.

• Blood flows back into LV during diastole, leading to increased SV
• This leads to increases SBP and decreased DBP. leading to a bounding pulse (Quinke’s sign) and LV hypertrophy.

Question 17

What are the causes and consequences of mitral valve regurgitation?

Answer 17

• Myxomatous degeneration can weaken tissue leading to prolapse
• Blood leaks back into LA, increasing preload, more blood enters LV in subsequent cycles, causing LV hypertrophy.

Question 18

What are the causes and consequences of mitral valve stenosis?

Answer 18

Causes = rheumatic fever (99.9% cases)
Consequences = Increased LA pressure leading to RV hypertrophy, or LA dilation which can lead to thrombus formation or dysphagia.